also in blepharitis. Lacritin is an LFU prosecretory mitogen and survival factor with a biphasic dose response that is optimal at 1 - 10 nM for human recombinant lacritin on human cells. Higher human lacritin concentrations are optimal on rat or mouse cells or on rabbit eyes. In a recent phase I/II clinical trial, a 22 µM topical dose of 'Lacripep' applied three times daily was effective at two weeks in primary Sjogren's Syndrome patients with an eye dryness score greater than 60, a score indicative of moderate to severe dry eye. Both corneal fluorescein staining and the symptom of burning/stinging were reduced. In keeping with a biphasic dose response, the 44 µM dose was largely ineffective. A biphasic dose response has a bell-shaped curve, with doses lower or higher than the dose optimum less effective. Other mitogens share this property. However, in secretion assays using monkey lacritin on monkey lacrimal acinar cells, the dose response appears to be sigmoidal with increasing lipocalin or lactoferrin secretion through a narrow 0.1, 0.3 and 1 μM dose range. Lacritin flows downstream from the lacrimal gland through ducts onto the eye. Artificial depletion of lacritin from normal human tears revealed that tears lacking lacritin are unable to promote the survival of ocular surface cells stressed with inflammatory cytokines. Human dry eye tears also lack this activity. However, dry eye tears supplemented with lacritin are fully protective. Similarly, tears artificially depleted of lacritin are deficient in bactericidal activity. The antibody used to deplete lacritin also depletes C-terminal proteoforms. These observations suggest that among all tear proteins, lacritin may be the master protector. Dry eye tears are subject to premature collapse, as are normal human tears artificially depleted of C-terminal proteoforms. In both cases, stability is largely restored by spiking in synthetic lacritin peptides N-94 or N-94/C-6 as proxy C-terminal proteoforms. Each peptide inserts rapidly into (O-acyl)-omega-hydroxy fatty acid (OAHFA) thought to reside at the aqueous lipid boundary in tears. OAHFA is the only class of tear lipids apparently downregulated in dry eye. Signaling Lacritin mitogenic, survival and secretion signaling have been studied. Lacritin mitogenic signaling follows two pathways: Gαi or Gαo → PKCα/PLCγ2 → Ca2+ → calcineurin → NFATC1 Gαi or Gαo → PKCα/PLCγ2/PLD1 → mTOR Rapid dephosphorylation of PKCα causes it to transiently move from the cytoplasm to the area of the Golgi apparatus and peripheral nucleus. Here, it forms a complex with